June 24, 2024

The Southern Pinwheel
By Richard Wright

We are deep in “galaxy season” in June with the early evening sky looking out along the arms of the Milky Way and deep into intergalactic space. There are many fine targets to choose from this month, and I’ve chosen a southern jewel known as the Southern Pinwheel that is due south as night falls for most of us in the northern hemisphere. Located in the southern constellation of Hydra, M83 is about 16 million light years away and is actually one of the closest and brightest spiral galaxies in the sky.

Although accessible from the Northern Hemisphere, this galaxy was discovered from the Cape of Good Hope in 1752 by Nichola-Louis de Lacaille and added by Charles Messier to his catalog as M83. This face on galaxy is a barred spiral and is reasonably bright as galaxies go and can even be seen visually in binoculars under dark skies with an apparent magnitude of 7.6. It’s not huge, but at nearly 13 arcminutes across it shows nice details at almost any focal length.

The image above was taken in South Florida, but M83 is still quite available to our friends in Canada if they have a clear southern horizon. As a brighter target, M83 does well with a one-shot color camera as well as using a monochrome sensor with filters. A hydrogen alpha filter on a monochrome sensor can supplement the color image with highlighted star forming regions along the spiral arms. The images here were all taken with an IMX533 based color camera, so monochrome is not necessary to reveal a great deal of color and details.

M83 can be a challenging target due to its low elevation, and you may find it easier to shoot with a monochrome camera as when very low the red, green, and blue components may not line up perfectly with a one-shot color camera (this is a common issue with shooting planets that are low on the horizon). On a quality APO refractor or mirror-based telescope however they should all be in focus simultaneously, and you may be able to separate the color channels and realign them in post processing with a tool such as PixInsight. I had exceptional conditions when I took this image with M83 being between 25 and 30 degrees above the southern horizon. Once I shot Eta Carina in the Florida Keys at only 4 degrees above the ocean, again under exceptional weather conditions. Remember in astrophotography rules of thumb (“never shoot less than 40 degrees, etc.”) are just… well as the pirates say, “more like guidelines really”! Always consider your sky conditions, and when those really great nights come along, go ahead and stretch your gear a little bit to do something out of the ordinary.

I really find M83 to be one of the most beautiful and often overlooked spiral galaxies in the Messier catalog. It is bright and colorful, the core shows amazing detail, and the spiral arms clearly stand out almost in 3D with dark ridges composed of dark dust lanes and bright knots of glowing star birth. What’s not to love about this galaxy? Careful processing and good seeing will also show distinctly a double star shown at about the 8 O’clock position in these images.

If you have sufficient focal length and exposure time, you may also pick up a few very tiny galaxies far behind M83. The two shown here are PGC 724525 and PGC 48132 (PGC stands for Principal Galaxies Catalog). PGC 48132 is a whopping 670 million light years away at a magnitude of 16.04, and PGC 724525 is 650 million light years away at a very faint magnitude of 17.02. Considering that M83 itself is less than 15 million light years distant, these guys are definitely galaxies “far far away”. In fact, the light from these two galaxies reaching us today predates dinosaurs by a staggering 400 million years!